Hi Tony,
Bebop's advice is sound advice. In the past I bought off-the-shelf systems (Packard-Bell) and learned the hard way that they leave a lot to be desired. They come with pre-loaded software, some of which you don't want or will never use but which you pay for nevertheless. You will find software titles you want, especially those related to recording music which you will have to pay for separately. Sound systems are basic as are the CD writers/players. But I think the biggest drawback is loss of flexibility (choice) and the inevitable expense when repairs are needed. Most off-the-shelf-systems have the sound cards, graphics cards, modems etc. physically mounted on the motherboard, thus making it very expensive to fix them if they fail. And very importantly, you cannot upgrade to a better sound or graphics card. If you have a system hand-built for you, you just remove the cover and replace a sound card or whatever fails and you are back in business. And if you want to upgrade it is as easy as ABC. Just remove the cover, plug in the new card and you are up and running.
My son is a computer whiz and built the system I am using at the moment. I've had it for nearly five years. I'm running Windows 98 with a 400 MHz microprocessor which will tell anyone that my system is "old" when compared to the super fast microprocessors available today. My system has performed flawlessly. But I am ready to upgrade now and have had a talk with my son about building a new system for me. We have talked about microprocessors, hard drives, sound cards, graphics cards, CDs, scanners, and printers, and have come up with a ballpark figure for a system that will give me "top of the range" performance in terms of processing speed, sound and graphics, the three main concerns for me.
I suggest you would be wise to follow the advice of some here and find someone you can trust to build a system for you rather than buying one off the shelf. In doing so, you can tailor your system to your needs in terms of sound, graphics, software, and CD playing/writing capability. And don't forget to include USB ports as part of your planning.
If you wish, I will have my son suggest some hardware options for you to consider. They will parallel my preferences in some cases since you and I have the same keyboard. You will need the correct software to backup midi files and create MP3 files as well as making recordings. However, it is the hardware that puts quality into the sounds you record while playing and singing, so careful selection of a microphone, sound card and CD writer/re-writer is key to that end.
In the end, what you are willing to pay will determine the quality and capability of your machine.
Good luck with your choice.
Chuck